In the operation of a rotary offset printing press, freshly printed substrates such as sheets or web material are guided by transfer cylinders or the like from one printing unit to another, and then they are delivered to a sheet stacker or to a sheet folder/cutter unit, respectively. As used herein, the term “transfer cylinder” includes delivery cylinders, transfer rollers, support rollers, support cylinders, delivery wheels, skeleton wheels, segmented wheels, transfer drums, support drums, spider wheels, support wheels, guide wheels, guide rollers and the like.
The ink marking problems inherent in transferring freshly printed substrates have been longstanding. In order to minimize the contact area between the transfer means and the freshly printed substrate, conventional support wheels have been modified in the form of relatively thin disks having a toothed or serrated circumference, referred to as skeleton wheels. However, those thin disc transfer means have not overcome the problems of smearing and marking the freshly printed substrate due to moving contact between the freshly printed substrate and the projections or serrations. Moreover, the attempts to cover the transfer cylinder with a cover material and/or minimize the surface support area in contact with the freshly printed substrate material often resulted in further problems.
Various efforts have been made to overcome the limitations of thin disk skeleton wheels. One of the most important improvements has been completely contrary to the concept of minimizing the surface area of contact. That improvement is disclosed and claimed in my U.S. Pat. No. 3,791,644 to Howard W. DeMoore, incorporated by reference herein in its entirety, wherein the support surface of a transfer cylinder in the form of a wide wheel or cylinder is coated with an improved ink repellent surface formed by a layer of polytetrafluoroethylene (PTFE).
During the use of the PTFE coated transfer cylinders in high-speed commercial printing presses, the surface of the coated cylinders must be washed too frequently with a solvent to remove any ink accumulation. Moreover, it has also been determined that the PTFE coated cylinders do not provide a critically needed cushioning effect and relative movement.
The limitations on the use of the PTFE coated transfer cylinders have been overcome with an improved transfer cylinder having an ink repellent, cushioning and supportive fabric covering or the like for transferring the freshly printed sheet. It is now well recognized and accepted in the printing industry world-wide that marking and smearing of freshly printed sheets caused by engagement of the wet printed surface with the supporting surface of a conventional press transfer cylinder is substantially eliminated by using the anti-marking fabric covering system as disclosed and claimed in my U.S. Pat. No. 4,402,267 entitled “Method and Apparatus for Handling Printed Substrate Material”, the disclosure of which is incorporated herein by reference.
That system, which is marketed under license by Printing Research, Inc. of Dallas, Tex., U.S.A. under the registered trademark SUPER BLUE® includes the use of a low friction coating or coated material on the supporting surface of the transfer cylinder, and over which is loosely attached a movable fabric covering. The fabric covering provided a yieldable, cushioning support for the freshly printed side of the substrate such that relative movement between the freshly printed substrate and the transfer cylinder surface would take place between the fabric covering and the support surface of the transfer cylinder so that marking and smearing of the freshly printed surface was substantially reduced. Various improvements have been made to the SUPER BLUE system, which are described in more detail in U.S. Pat. Nos. 6,244,178 and 5,907,998 each entitled “Anti-Static, Anti-Smearing Pre-Stretched and Pressed Flat, Precision-Cut Striped Flexible Coverings for Transfer Cylinders”; U.S. Pat. Nos. 6,119,597, 5,603,264, 6,073,556, and 5,511,480 each entitled “Method and Apparatus for Handling Printed Sheet Material”; U.S. Pat. No. 6,192,800 entitled “Method and Apparatus for Handling Printed Sheet Material”; and U.S. Pat. No. 5,979,322 entitled “Environmentally Safe, Ink Repellent, Anti-Marking Flexible Jacket Covering Having Alignment Stripes, Centering Marks and Pre-Fabricated Reinforcement Strips for Attachment onto Transfer Cylinders in a Printing Press”, each of which is hereby incorporated by reference herein in its entirety.
Despite the advantages of my previously described anti-marking systems, the printing industry continues to use obsolete transfer cylinder cover materials such as T-Y paper and non-tack film. T-Y paper comprises a paper backing with grit laminated thereon, producing a laminate material resembling sandpaper, and is sometimes referred to as sphere-coat or gem-kote. Non-tack film comprises a film backing such as polyester with silicon beads laminated thereon, also producing a gritty, sandpaper-like material sometimes referred to as Pearl-Tex, Spectra film, or ICP film. T-Y paper and non-tack film are releasably attached to a transfer cylinder, for example by clamps on the transfer cylinder or by use of a spray adhesive or a double sided tape, and support a printed substrate traveling through a printing press. During the printing process moisture from the printed sheets, in the form of ink as well as moisture from the dampening system, is in contact with the gritty surface of the T-Y paper and non-tack film. The dampening system is the system by which ink, water, and other additives such as ink repellant chemicals are transferred in sequence to a plate cylinder, a blanket cylinder, and a printed sheet. Over time, the moisture from the printed sheet will begin to penetrate the gritty surface and/or accumulate thereon, thereby limiting the service life of the cover material. As the moisture penetrates the gritty surface, the cover materials, and in particular T-Y paper, begin to weaken and ultimately tear and fail. As ink accumulates on the gritty surface, the printed substrates may be undesirably marked and flawed by the accumulated ink, or the accumulated ink may flake off and cause press problems such as “hickeys” on the plate cylinder, the blanket cylinder, or both. In particular, portions of the gritty material or clumps of ink may accumulate on a blanket, plate, or impression cylinder causing unwanted small printing imperfections commonly known as “hickeys” to appear on the printed substrate. In order to reduce the accumulated ink, the T-Y paper and non-tack film may need to be cleaned, for example by wiping down the gritty surface with a sponge or solvent rag. While cleaning may temporarily help reduce ink accumulation, the cleaning further subjects the gritty surface material to moisture, thus accelerating the moisture penetration problem and further shortening the service life of the cover materials.
T-Y paper and non-tack film typically need to be regularly maintained, cleaned during a press stoppage, and periodically replaced. Regular maintenance is the regular washing and cleaning of the T-Y paper or non-tack film according to the manufacturers recommendations, which is typically at the end of a daily shift to avoid having ink dry on the covers between shifts or overnight. A printing press may have to be stopped during a run to clean of one or more cylinders in the press in order to remove accumulated ink or contaminants thereon that are causing an imperfection such as a hickey on the printed sheet, as discussed previously. Periodic replacement is the replacement of the T-Y paper or non-tack film as they wear out and are no longer operable. Regular maintenance, cleaning during a press stoppage, and periodic replacement lead to costly press down time and additional expenses. For example, a 4 color printing press may have from 6 to 8 transfer cylinders (and in particular a 4 color press made by Komori Corp. may have 6 or 8 transfer cylinders). A conservative estimate for the amount of time required to wash a single transfer cylinder is 3 minutes, and thus it can easily take 18 minutes during an 8 hour work-shift for regular maintenance of T-Y paper and non-tack films on 6 transfer cylinders. Also, it is not uncommon to have to stop the press at least once during a shift to clean at least one cylinder (i.e., transfer cylinder, blanket cylinder, or plate cylinder) due to printing imperfections associated with T-Y paper and non-tack films, which would add even more lost press time. According to the Printing Industries of America, Inc.'s 1998 Production and Cost Standards Report, a typical, 40 inch four-color offset printing press has an all inclusive hourly cost rate of from about $300 to $500 per hour. Thus, a printing press operator may easily lose $90 per day (18 minutes×$5/min.) or more in press down time due to cleaning associated with T-Y paper and non-tack films, which typically increases with an increase in the number of shifts. Over the course of a year, a press operator may easily lose in excess of $20,000, which grows to in excess of $100,000 over a five-year period. Stopping a press for cleaning leads to wasted materials and additional losses and/or costs, as a number of printed substrates are typically off-specification (e.g., color and/or registration) and unsalable following re-start of the printing press. Also, the T-Y paper typically needs to be replaced at a frequency ranging from weekly to monthly at a price of about $16–30 per change per cylinder for a 40 inch press, and the non-tack film typically needs to be replaced about every three months at a cost of about $100 per change per cylinder for a 40 inch press. The present invention advances the state of the art by providing an inexpensive, wash-free, disposable, easy to install transfer cylinder cover that reduces or eliminates the problems and expenses associated with T-Y paper and non-tack films.